Handle null GIF input with IOException

[blihio]

Problem

GifFilterRender.setGif accepts InputStream?, but GifStreamObject.load immediately calls available() on it. Passing null therefore raises an unexpected NullPointerException before GIF decoding starts.

Change

Reject null at the start of GifStreamObject.load with IOException, using the existing GIF loading error path. This preserves the Kotlin nullable parameter and existing JVM method signatures.

Add GifFilterRenderTest.nullInputIsReportedAsIoException to exercise the public Kotlin API. It fails with NPE on the original code and passes after this fix.

Validation

With only this change applied to base commit 82a9cb4ee4babdc792d2ccee8b893f2b36207d40, using Gradle 9.7.1 and JDK 17:

./gradlew :common:testDebugUnitTest :encoder:testDebugUnitTest

• common: 98 tests passed.
• encoder: 26 tests passed.
• git diff --check passed.

A supplementary JVM check also loaded a valid one-frame 1×1 GIF using the real decoder before and after the fix. That check uses an in-memory Android Bitmap stand-in; device rendering was not tested.

Fixes #2216

[pedroSG94]

Thank you for the PR. Merged